1. Field of the Invention
This invention relates to material handling industrial trucks and is particularly suitable for an industrial truck which includes a mobile frame having a centrally located mast or upright structure upon which a load carriage is mounted for lifting and lowering movement. The load carriage may include an operator's station which moves upwardly and downwardly with the load.
2. Description of the Prior Art
The industrial truck mentioned is of the counterbalanced or non-straddle type. The frame extends sufficiently to the front and rear of the centrally located mast structure, and laterally, to provide vehicle stability. At the front of the machine is located a drive unit assembly which is pivotally connected to the truck frame and which includes a drive-steer wheel for steering, propelling and braking the machine. At the rear of the vehicle pairs of unidirectional support wheels are located on the frame.
It is known to assemble a non-counterbalanced or straddle type industrial truck from some of the same sub-assemblies or modules that are used for counterbalanced type trucks. In the straddle type industrial truck, the frame is lengthened at the rear and the frame is ordinarily equipped with caster wheels near the outer forward edges thereof and laterally of the drive-steer wheel. Outrigger portions are added to the rear sides of the frame, the rear end being supported by a pair or pairs of uni-directional wheels.
U.S. Pat. No. 3,756,350, Gandolfo et al., dated Sept. 4, 1973, discloses industrial truck modules which can be assembled to form either the straddle type or the counterbalanced type industrial truck described above. The industrial truck shown in FIGS. 1, 3 and 5 of that patent is of the straddle type while that shown in FIGS. 2 and 4 is the counterbalanced type. The present invention is adapted to be used with either the straddle or counterbalanced type industrial truck.
Heretofore in order selector type lift trucks as herein contemplated various means have been utilized to adjust the upright to predetermined vertical or tilted positions as required for satisfactory operation with varying load induced upright deflections, tire wear factors and the like. In order selector trucks wherein the operator's station is located on the elevatable load carriage from which all operating components of the truck are controlled it is desirable to adjust the upright to, for example, a vertical angle between 0.degree. and 1.degree. back-tilt. On newly assembled vehicles such an adjustment is necessary to compensate for manufacturing tolerances and the variations in vehicle weight and center of gravity locations, as well as for any back-tilt resulting from upright extension. Over a period of time of lift truck operation any change in the vertical position of the upright due to the normal wear of such components as tires and upright rollers may require such an upright adjustment from time to time.
Most, if not all, of standard four-wheel, sit-down, counterweighted type lift trucks wherein the upright is mounted at the front of the truck utilize hydraulically operable tilt cylinders for tilting the upright and the load forwardly and rearwardly to compensate for load induced upright deflections and for use in picking up, transporting and depositing loads.
Lift trucks of the narrow aisle and order selector type as herein disclosed utilize an upright that is fixedly secured to the chassis or truck frame with adjustment of the vertical position of the upright during manufacture and assembly of the truck being effected by various known means. Such known means may include adjustment of the upright by shimming flange bolted connections thereof to frame support members such as, in practice, may be done in the structure of the above Gandolfo et al. patent by locating shims between the upright flanges and upright frame support members adapted to be connected thereto.
Another structure used by certain manufacturers is shown on the enclosed specification sheet entitled "Frame and Mast Assembly" whereon applicant has added the legend "Outriggers welded at slight downward angle", which permanently effects one desired tilt angle.
Again, the tilt angle may be varied by mounting the upright on trunnions for pivotal movement and utilizing "turn-around" brackets, such as in U.S. Pat. No. 3,378,159, Trusock, dated Apr. 16, 1968.
Copending application Ser. No. 260,969, Jones, filed May 6, 1981 now U.S. Pat. No. 4,431,084, common assignee, discloses a lift truck of the same general configuration and structure as herein, but for a straddle type vehicle wherein in one embodiment a sole fixed adjustment position of the upright is provided in contrast to the multiple adjustment positions thereof as provided by my invention.
In the specially welded assembly above referred to upright readjustment is not possible, and in the patented structures noted above it is difficult and time consuming. In the above mentioned copending application no provision is made for such upright adjustment. Furthermore in none of the above adjustable upright constructions does the resulting structural connection between the upright and the frame substantially increase the overall lateral structural rigidity of the upright, which is effected in my invention by adding the structural lateral rigidity of the truck frame to the lateral rigidity of the upright. My construction also provides a relatively easy means for adjusting the upright vertical angularity.